1. Field
The present disclosure relates to communications systems, and amongst other things, to systems and techniques for packet routing in wireless communication systems.
2. Background
Traffic on the Internet is growing exponentially due to an increasing number of subscribers and the introduction of new applications. Wide area wireless networks are also experiencing rapid subscriber growth. Currently, there are many efforts underway to provide data services on wireless access networks.
To facilitate data services in mobile wireless telecommunication systems, it is desirable to allow mobile wireless nodes to change their link-layer point of network attachment without reassigning a new network address. According to current data network telecommunication standards for mobile equipment in general (e.g., the “Mobile IP” standards promulgated by the Internet Engineering Task Force (IETF) or the General Packet Radio Service (GPRS) standards proposed by the European Telecommunication Standards Institute (ETSI)), one way to provide the desired network address transparency is to employ “mobility agents.” These are network routing nodes that route communication content on behalf of mobile nodes as they move around the network. For example, according to the IETF Mobile IP standards, a mobile node's mobility agents may consist of a “home agent” routing node and may also include a “foreign agent” routing node. The home agent is a routing node in the mobile node's sub-network that maintains a network interface on the link indicated by the mobile node's “home address,” which is a network address intended to remain assigned to the mobile node for an extended time period. When the mobile node is away from its home sub-network, the home agent intercepts communication content bound for the mobile node's home address and tunnels it for delivery to a “care-of” address assigned to the mobile node when the mobile node registers on a foreign sub-network. The care-of address may be the address of a foreign agent routing node in the foreign sub-network.
Correspondent nodes wishing to communicate with a foreign-registered mobile node are able to address their communication content to the mobile node's home address. Transparently, the communication content is intercepted by the home agent and tunneled to the mobile node's care-of address and delivered to the mobile node on the foreign sub-network. Normal routing may be used for sending return communication content from the mobile node to the correspondent node.
The foregoing routing mechanism can be used for mobile wireless nodes connected to a foreign sub-network via an air interface. However, a problem may arise if the mobile wireless node is being actively transported while communicating over the data network and a call handoff is required from one radio base station to another. In that case, the old base station may be linked to one care-of address, while the new base station is linked to another care-of address. Call handoff then requires that the communication tunneling endpoint be transferred from the old care-of address to the new care-of address.
Further, in some cellular telephony architectures a care-of address end point located in the core network is utilized as the addressed communication, e.g. target Internet Protocol Address, for data communication with a wireless communication apparatus or terminal. In some instances, the end point may be a packet data service node (PDSN), a base station controller (BSC) or the like. A handoff between PDSN end points may be required to maintain a minimum level of communications with the mobile wireless node, for instance due to conditions in the core network such as congestion or latency to the mobile wireless node. PDSN handoff then requires that the communication tunneling endpoint be transferred from the care-of address of the old PDSN to the care-of address of the new PDSN.
Transferring the tunneling endpoint of the care-of-address may create gaps that interrupt the timely delivery of call content, or result in out-of-order delivery of content, both of which can degrade communication quality, particularly for voice telephony. Such gaps arise from the inability of the data network to coordinate well with the air interface so as to determine the exact time of handoff. Reorderings can arise when a new tunnel endpoint is significantly closer to the home agent than the old tunnel address. Delay can occur between the point of handoff and the point at which the home agent begins routing communication content to the new care-of address.
Accordingly, there is a need in a data network telecommunication system serving mobile wireless nodes for improved call handoff without loss of communication content. There is a need for systems and methods that route communication content during handoff so that a wireless device does not experience noticeable communication content loss other than that caused by the air interface, if any.